1. Field of the Invention
The present invention relates to a time/date adjustment device for a computer equipped with a satellite broadcast receiving subsystem.
2. Description of the Related Art
Conventionally, a known system of time/date adjustment device is based on a technique of inputting time information received from a satellite into a computer, as disclosed in a Japanese Patent Application, First Publication Hei 7-55965. This method is predicated on having an earth-orbiting satellite which periodically outputs information including global standard times, and a computer receiving this information computes a time difference according to the receiver coordinates relative to the orbiting satellite, and adjusts the time stored inside the computer.
Another technique is suggested in a Japanese Patent Application, First Publication Hei 5-119170, which is based on receiving a time signal output from a broadcasting satellite, and correcting it for the propagation time difference of the signal at the receiving location. In this method, delay time difference from the standard time, caused by the propagation differences corresponding to the latitude/longitude of the receiving location, is stored in the computer, and the delay time is corrected with reference to the time signal contained in the received satellite signal and a trigger signal output by the receiving computer.
Japanese Patent Application, First Publication Hei 8-316858 discloses a technique for correcting the time based on the standard time data in the teletext data. Japanese Patent Application, First Publication Hei 9-061561 discloses a technique for correcting the time based on the information included in the television signal. Japanese Patent Application, First Publication Hei 9-119992 discloses a device which reproduces a clock pulse and a time data from the signal transmitted from the GPS satellite and outputs an accurate time data. Japanese Patent Application, First Publication Hei 59-165116 discloses a timer in a computer for correcting the time based on the error which is measured in advance.
However, the technology disclosed in the Japanese Patent Application, First Publication Hei 7-55965 has the following problems. First, it is predicated on the use of an orbiting satellite generating the global standard time signals, but such a satellite does not exist in reality. Further, satellites used in broadcasting are geostationary satellites, and are intended for use in relaying programming schedules and time information from terrestrially based broadcasting stations, and beaming the information back to the earth surface. Thus, the signals do not contain any information that can be used to determine the coordinates of the receiving location.
Second, depending on the time information output from the satellite, the satellite time cannot be synchronized with time signals sent from the earth, and therefore, cannot be synchronized with earth-based broadcast programs. Thirdly, because date information is not output by the satellite, the earth-based computer cannot receive date information. Fourth, the receiving computer cannot be powered simply by setting the computer time to the satellite time, therefore, if a time-activated signal reception is required, satellite information must be received while the power to the computer is turned on.
In the technology disclosed in the Japanese Patent Application, First Publication Hei 5-119970, trigger signals (=time signal) are pre-determined depending on geographic locations, and to correct the time, the trigger signal is delayed slightly depending on the longitude of a receiving location. For a program whose broadcast is synchronized to the correct time, a gap is created between the program and the correct time, so that the correction method is not preferable in consideration of timer starting. Therefore, for the case of synchronizing actual broadcasting to the correct time, this technique is meaningless.
It is an object of the present invention to provide a time/date adjustment device for automatically synchronizing the time data in a computer receiving a satellite broadcast program with the time/date information transmitted by electrical wave from satellite.
The object has been achieved in a time/date adjustment device for adjusting time/date data of a computer in a computer system, equipped with a satellite broadcast receiving subsystem, comprising: a time/date receiving section for receiving broadcast time/date information transmitted from a satellite; a decoding section for decoding the broadcast time/date information; and a write section for writing decoded time/date data to a real-time clock circuit backed by a battery that manages time data in the computer.
It is preferable that the decoding section is a stream separation device, provided in the satellite broadcast receiving subsystem, for separating time/date data from multiplexed signals, received from the satellite, comprised by video data, audio data and other signals. Also, the write section may serve as an interface means between satellite broadcast receiving subsystem and an operating system, and represents a driver software operated by the computer.
It is preferable that the computer is provided with: a timer-activation time register for storing time data to enable time-activating the computer even when a main power source for the computer is off; a comparison section for comparing time/date data in the real-time clock circuit with time data stored in the timer-activation time register, even when the main power source for the computer is off; and a power request section for outputting a power request signal to power the computer based on a comparison result, when the main power source for the computer is not on.
A first advantage of the time/date adjustment device is that the current time being managed in the application software for satellite broadcast reception, and the time data which had been stored in the computer are now unified, so that there is no need for using a time-based application software to adjust the computer time data. The reason is that the time data in the computer is automatically synchronized to the time/date information received in the computer from a broadcast satellite. A second advantage is that when the software for satellite broadcast reception is to be timer-driven by the computer, there is no need to constantly receive time/data information from the satellite. This is because the time/date information received from the satellite is synchronized with the time/date data in the real-time clock in the computer is back up by a battery so that, even when the computer power is off, the time is functioning correctly.